Software Engineering Institute

Exim is a message transfer agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet. The internal string handling functions of the Exim software contain a function called string_format(). The version of this function included with Exim versions prior to 4.70 contains a flaw that can result in a buffer overflow. An attacker can exploit this vulnerability by crafting message headers that are subsequently supplied to Exim logging functions.

Note: this vulnerability has been reported being exploited in the wild.

A remote, unauthenticated attacker may be able to execute arbitrary code with the privileges of the Exim server. A separate vulnerability in Exim could then allow the attacker to escalate privileges to root.

Apply an update

Users who obtain Exim from a third-party vendor, such as their operating system vendor, should see the vendor information portion of this document for a partial list of affected vendors.

This vulnerability is reportedly addressed in Exim version 4.70. Users of Exim from the original source distribution should upgrade to this version or later, as appropriate. Users who are unable to upgrade are encouraged to apply the following patch from the Exim developers:
<http://git.exim.org/exim.git/commitdiff/24c929a2>